Centrifugal pump for fluids containing solid materials, and gap seal

ABSTRACT

The proposed rotary pump for transporting liquids containing solids is composed of a pump housing ( 1 ) and an impeller ( 2 ) disposed on a rotating driven shaft. The pump housing ( 1 ) encloses a flow space having an intake region ( 4 ) and having a pressure region ( 5 ) surrounding the periphery of the impeller ( 2 ), as well as also a back space ( 6 ) of the impeller. According to the invention, the gap ( 3 ) relative to the back space ( 6 ) of the impeller is completely sealed opposite the flow space relative to the transported liquid with the solids contained therein, wherein, however, there is provided a connection of the back space ( 6 ) of the impeller to the pressure region ( 5 ), by which its aeration and venting are made possible. 
     Essential elements of an arrangement for sealing the gap ( 3 ) are: a sliding surface ( 10 ) formed on the impeller ( 2 ), an at least partially elastic sealing element ( 9 ) sliding along by its end ( 11 ) on the sliding surface ( 10 ), as well as means ( 15, 15′, 16, 16′, 17, 17′, 18, 18′ ) for the aerating and venting of the back space ( 6 ) of the impeller, wherein the sealing element ( 9 ) is fixed in place on a pressure cap ( 12 ) closing the pump housing ( 1 ) on the side facing away from the intake region ( 4 ).

The invention relates to a rotary pump having an impeller mounted on one side for transporting liquids containing solids and an arrangement for sealing a gap in such a rotary pump. It preferably refers to, but is not limited to, a solution for rotary pumps for wastewater transport, thus for transporting water contaminated with solids.

In rotary pumps, the respective medium is transported by means of at least one impeller moving in a pump housing and disposed on a shaft driven in rotation. By means of the rotating impeller, the transported medium is drawn to an intake side of the pump to a certain extent into the impeller, namely into the space between rotating blades formed on the impeller, and transported to a pressure side of the pump, where it is again discharged from the pump through a corresponding outlet opening. In order for the impeller to be able to move in the pump housing, gaps between the impeller and the inside of the pump housing on the front side of the impeller, thus in the intake region of the pump, and on the impeller pressure side are indispensable. On the other hand, however, a number of problems result from the requirement for these gaps. Thus, a portion of the transported medium inevitably passes back through the gap to the front side of the impeller due to the prevailing pressure difference, from the pressure side to the intake side of the pump, which is equivalent to the formation of hydraulic losses.

Also, flow components of the transported medium reaching into the back space of the impeller imply a hydraulic loss that leads to a reduction in efficiency. In particular, when rotary pumps are used for transporting wastewater or other media contaminated in any way by solids, however, another problem moves more into focus, a problem that is associated with the gap on the back side of the impeller. This problem consists of the fact that solids, i.e., solid, particularly fibrous, contaminants, such as those that are continually found in wastewater, basically tend toward engulfing one another or intertwining with one another, and/or entwining with the impeller and the shaft. Due to this process, which is called braid formation, the gaps can fill up, so that the impeller becomes blocked, or a direct blockade of the drive shaft can also occur in this way. As a result of this, interruptions in operation occur and there is often great damage or even a complete breakdown of the pump. Corresponding damage must be prevented or, insofar as it has already occurred, must be eliminated by expensive maintenance and repair measures. The risk of the occurrence of such damage increases with the operating time of the pump, within which solid contaminants or components of braids forming on the impeller burn onto it and onto the inside of the pump housing, due to thermal effects.

Over the years, solutions have thus become known, by means of which the adverse effects arising due to braid formation, which are discussed above, will be countered, particularly in the region of the gap in the front side of the impeller or in the intake region. It has thus been attempted to keep this gap as small and as constant as possible or to close it, preferably at least to a great extent, against a transport of material by using so-called gap rings or by other measures. Appropriate measures are clearly made difficult due to the manufacturing tolerances of the components of the rotary pumps and due to strong axial and radial oscillations or impeller excursions both in the axial as well as in the radial direction that occur particularly in rotary pumps with an impeller mounted on one side during their operation. It has also been shown that measures for reducing the gap and thus bringing about an extensive suppression of the transport of material are finally not sufficient for being able to effectively overcome the problem of a blockage of corresponding pumps and thus, possibly also their damage over longer time periods of operation.

In contrast, measures for sealing on the back side of the impeller so that it is assured that the transported medium does not exit from the pump housing on this side or move in the direction of the equipment driving the shaft are ostensibly limited. Accordingly, the motor and the chambers for the uptake of oil necessary for the lubrication of the system, the so-called oil chambers, are particularly sealed opposite the transported medium, and hydraulic losses are reduced thereby. A transport of material, i.e., a flow of the transported medium containing solids and contaminants through the gap to the back space of the impeller, however, is not suppressed in this way.

On the other hand, one has recognized within the scope of practical experience associated with eliminating disruptions occurring in operation that there exists the problem of a possible braiding of contaminants also in the back space of the impeller. This has led to the opinion that care should be taken in the back space of the impeller to preferably produce a targeted turbulence of the transported medium or of the transported liquid, in order to avoid a braid formation as much as possible by means of the constantly moving medium. An example of solutions created for this is given by the wastewater pump described in DE 29 00 434 A1. The solution disclosed in the publication is based on producing a radially extending rotating liquid screen by means of an additional blade ring disposed behind the impeller, which, for example, shall keep solids contained in the wastewater away from the impeller and the drive shaft.

It is precisely the functional principle of the rotary pump that represents the real problem with respect to transporting liquids encumbered with solid contaminants. Due to the pressure gradients in the actual pump, in the region of the highest pressure, the transported liquid is semi-aspirated through the gap between the back of the impeller and the pressure cap (“intake connection”), and an exit site (“pressure connection”) is found again in the lowest pressure zone of the gap in the pump housing space. Thus, liquid is transported continually in a targeted manner into this “hydraulic dead space” of the pump, but in an uncontrolled and energy-destroying, abrasive way, tending toward blockage. The widely distributed radial back blades have a similar perverse effect in the operation of wastewater rotary pumps. Instead of eliminating the blockage problem, solid blockage material is entrained first through the forced flow through the back space of the impeller, and as a consequence of the uncontrollable flow processes, braid formation, blockage, and finally the burning on of solids are to a certain extent forced. In addition, due to the abrasive components, erosion that is in part too deep occurs, even with formation of holes, thus leading to costly failure of the rotary pump. All of the solution approaches that have as content the flow through the back space of the impeller thus do not lead to the goal. Rather, they require additional, internal drive power due to the described “bypass flow transport” and thus cause a reduction in efficiency.

Also, another approach to the solution, which is described, for example, by DE 20 51 011 A1 has not proven suitable in practice for fully preventing a braid formation in wastewater pumps on the back side of the impeller. The solution described in the publication, like comparable solutions, derives from a labyrinth system formed on the back side of the impeller, by means of which very narrow gaps are provided, which equilibrate, within certain limits, the oscillations occurring during operation of the pump. However, since parts of the transported, impeller-vortexed medium and the contaminants contained therein additionally gain access into the back space of the impeller due to the gap on the back side, a stalling of the impeller due to the deposited and sometimes braided contaminants in the gap is not reliably excluded thereby.

Another approach, as is represented in JP 57024491 A, wants to prevent the entrainment of material behind the impeller by means of a special impeller geometry, but without sealing the structurally necessary gap and thus also preventing the unnecessary flow through the back space of the impeller that generates losses.

Further, a rotary pump with a seal arrangement for the gap formed in the back space of the impeller of the pump is known from DE 296 19 742 U1. According to the described solution, a freely movable, elastic sealing element is disposed inside the gap between two rigid elements, the first of which is connected to the back wall of the impeller, and the second being connected to a guide vane disposed in the pump housing. Here, the sealing element is distanced from the last-named rigid element and is pressed in a frictional contact against a surface of the other rigid element moved with the impeller due to the pressure of the fluid transported by means of the pump. It is stated in the publication that only small leakage losses still occur due to this type of arrangement of the sealing element. The distance that is present to the rigid element by means of which the free mobility of the sealing element is made possible, however, disadvantageously forms to a certain extent a type of secondary gap, in which solids can be deposited during the transport of contaminated liquids such as wastewater. Thus, there is the danger that such depositing solids clump together or cake up and adversely affect or even completely hinder the necessary mobility of the sealing element, so that, in particular, oscillations that also occur can no longer be sufficiently equilibrated. As a consequence, the frictional contact of the sealing element with the rigid element loosens at one or more weakest points (is possibly also only temporarily repeated) and thus leads to a reduction of the sealing effect. This in turn leads to the circumstance that additional solids are entrained into the gap region and the previously described effects are intensified yet further. In this respect, it results that the arrangement in fact functions well with a transport of pure liquids, but it may be rather unsuitable for the transport of liquids contaminated with solids, in particular of wastewater, since it does not appear suitable for permanently suppressing a transport of material.

The object of the invention is to avoid the above-mentioned disadvantages. By means of the solution that will be given for this, a braid formation and a settling of contaminants in the gap region of the back space of the impeller of a rotary pump serving for the transport of liquids containing solids and having an impeller mounted on one side will be reliably prevented, so that a very slow, disruption-free operation of the corresponding pump is made possible, in particular, even with its use as a wastewater pump. For this purpose, a correspondingly designed rotary pump and an arrangement for gap sealing of such a rotary pump will be provided.

The object is achieved by a rotary pump having the features of patent claim 1 and an arrangement for the gap sealing according to patent claim 2*. Advantageous embodiments or enhancements are given by the subclaims. sic; patent claim 3?—Translator's note.

The rotary pump for transporting liquids containing solids, particularly liquids contaminated with solids, which is proposed for achieving the object, as is basically known, is composed of a pump housing and an impeller mounted on one side, which is disposed in the pump housing on a rotating driven shaft, and is thus mobile. The pump housing has a media inlet opening and a media outlet opening. It encloses a flow space having an intake region on a front side of the impeller facing the media inlet opening and having a pressure region surrounding the periphery of the impeller. Further, a back space of the impeller that is formed on the side of the impeller facing away from the media inlet opening is enclosed by the pump housing. According to the invention, the gap relative to the back space of the impeller is completely sealed opposite the flow space with respect to the transported liquid with the solids contained therein, by means of a sealing element sliding along by an elastic end on a sliding surface of the impeller. In addition, however a connection of the back space of the impeller to the pressure region of the flow space is provided, through which an aerating and venting of the back space of the impeller is created.

Accordingly, the invention is based on the consideration that it is possible to completely seal the gap relative to the back space of the impeller against a transport of material from the pressure region of the flow space into the back space of the impeller, thus deviating from the solutions known from the prior art, as long as care is taken at the same time to aerate and vent the back space of the impeller; and thus, if air or gas bubbles should arise, there will be a pressure equilibration relative to the pressure region of the flow space. Unlike in the prior art, which involves counteracting a braid formation by a targeted production of a vortexed flow in the back space of the impeller that purportedly avoids this, the invention prevents this instead by a sealing solution that not only serves for the purpose of protecting a motor driving the drive shaft for the impeller, oil chambers or the like from the penetration of transported medium or transported liquid as is known from the prior art. Hence, it Is not only a reduction or optimizing of the gap that is provided, but rather a complete sealing of the gap relative to the back space of the impeller against a transport of material. Due to the last-named measure for the pressure equilibration, it is thus assured that the sealing element sliding along by its elastic end on the impeller keeps the gap permanently closed during the operation of the pump and the sealing effect is not adversely affected or damaged due to air or gas bubbles that form.

Also, the arrangement relative to the gap sealing proposed for achieving the object is subordinated to this consideration and thus to the basic inventive idea with respect to its nature. Therefore, the arrangement is configured, as has already been mentioned, so that the back gap is completely closed and this prevents solids or contaminants from accumulating in the region of the sealing element, i.e., in the gap region, a situation which finally could lead again to an undesired occasional or even permanent opening, of perhaps only a very small gap, upon longer operation of the pump.

Essential elements of the arrangement formed correspondingly are, accordingly, an at least partially elastic sealing element and a sliding surface formed on the impeller of the rotary pump equipped with the arrangement. During operation of the rotary pump, an elastic end of the sealing element slides along on the sliding surface formed on the impeller. In a large segment of its span, it is applied flat on the sliding surface. According to the invention, the sealing element is fixed in place on a pressure cap closing the pump housing of the rotary pump on the side facing away from its intake region, whereby the sliding surface is disposed on the impeller in the region of the back gap, i.e., a gap that is formed in the region of the back space of the impeller. The arrangement proposed for achieving the object according to the invention further comprises means for aerating and venting this back space of the impeller. Preferably, when the pump housing is closed by means of the pressure cap, the elastic end of the sealing element is pressed onto the sliding surface of the impeller, whereby the pressure cap, due to the fact that the sealing element is fixed on it, is a component of the proposed arrangement. Based on the elasticity of the end of the sealing element, axial and radial oscillations, which cannot be avoided during the operation of the pump, are effectively equilibrated, without the gap in the region of the back space of the impeller being opened temporarily thereby for a transport of material. The arrangement formed as described above for the gap sealing is suitable both for manufacturer's factory equipment (original equipment) as well as for a corresponding retrofitting of rotary pumps. In this case, the possibility of retrofitting in a special way is favored by the fixing in place of the sealing element onto the pressure cap closing the pump housing. In the sense of such a retrofitting, as can be recognized from the explanations given below, in a relatively simple way, the sliding surface can be created by corresponding post-processing of the impeller, and the means for the pressure equilibration can be provided by a corresponding formation of the sealing element or by a post-processing of the pressure cap.

An essential element of the solution according to the invention is to be seen in the fact that the end of the sealing element sliding along on the low-wear sliding surface of the impeller is designed as elastic. Elastomer materials, in particular, such as polyurethane, for example, have corresponding elastic properties. Accordingly, in a practical embodiment of the invention, at least the above-named end of the sealing element is composed of an elastomer, such as polyurethane, for example. It is also conceivable, however, to form the sealing element for the most part or even completely from an elastomer. An advantageous embodiment is given in this connection in that the regions of sealing elements composed of elastomer are interlaced by a fabric, at least in sections. In this way, the sealing element is mechanically stabilized and its service life or life span is increased.

Different possibilities are given for fastening the sealing element to the pressure cap. For example, the sealing element can be fastened to the pressure cap cohesively, for example, by adhesives or vulcanization. Corresponding to a preferred embodiment, the sealing element is fixed in place, however in a force-fitting or force-fitting and form-fitting manner to the pressure cap.

In particular, the sealing element can also be formed in various ways with respect to its shape as a function of the rest of the construction of the rotary pump equipped with the arrangement according to the invention for gap sealing. According to one embodiment provided thus far, the sealing element is formed as an elastomeric sealing ring, which slides along by a first axial section on the sliding surface of the impeller, and is pulled up onto a section or shoulder of the pressure cap projecting into the back space of the impeller by a second, conically tapering axial section relative to the diameter, according to an advantageous enhancement of this embodiment. In this way, the elastic end of the sealing element sliding along on the sliding surface of the impeller is formed by the above-named first axial section. Such an embodiment is particularly considered, if the impeller, on the one hand, and the shoulder of the pressure cap onto which the sealing element preferably composed completely of an elastomer is pulled with the formation or a force fit or a force and form fit, on the other hand, have nearly identical diameters.

In the case of the described embodiment corresponding to a first possibility, the aerating and venting of the back space of the impeller are provided such that in the pressure cap relative to its periphery, on at least each of two positions, behind the section of the sealing element pulled onto the pressure cap, a first borehole is formed extending in the radial direction into the material of the pressure cap, and a second borehole is formed extending from the back space of the impeller in the axial direction up to the first borehole. In this way, a channel is formed to a certain extent by the two boreholes running into each other, by means of which the pressure equilibrium can take place, for example, when the rotary pump is first filled with liquid. Another possibility for aerating and venting the back space of the impeller in the embodiment equipped with an elastomeric sealing ring as the sealing element consists of forming a radially extending passage to the back space of the impeller on at least each of two positions in the sealing ring relative to its periphery. The at least two passages in question are accordingly formed in the transition region between the first axial section forming the elastic end and the second axial section of the sealing element that is pulled onto the pressure cap.

In another embodiment of the arrangement according to the invention relative to the design of the sealing element, which is particularly provided for such rotary pumps, in which an axial end of the pressure cap projecting into the back space of the impeller has a greater diameter than the impeller, the sealing element is formed as a sealing collar gripping a shoulder of the pressure cap from behind. In this way, by means of this sealing collar, the different diameters of pressure cap and impeller are equilibrated by a section of the sealing collar extending in the radial direction. According to a preferred enhancement of this embodiment, the aerating and venting of the back space of the impeller are achieved by a special configuration of the above-named sealing collar. Here, in the section of the sealing collar extending in the radial direction, relative to its periphery, on each of at least two positions, a passage is formed, projecting through the radial section in question in the axial direction. In addition, in the region of the above-named at least two passages on the side of the radial section of the sealing collar facing the pressure cap, at least one support or one support point is formed, which is composed of the material of the sealing collar and projects in the axial direction. Preferably, in fact, four such supports are provided at uniform distances relative to one another on the periphery of the sealing collar. A flat hollow space is formed to a certain extent between the surface of the radial section of the sealing collar facing the pressure cap and the pressure cap due to these supports or support points. A pressure equilibration or an aerating and venting of the back space of the impeller can be produced via the above-named passages formed in the radial section of the sealing collar and the flat hollow space, for example, when the pump is first filled with the liquid to be transported.

In the case of a complete formation of the entire sealing element from elastomer and its fixing in place on the pressure cap, an additional cohesive fixation can be achieved advantageously by joining the sealing element adhesively with the pressure cap by vulcanization.

Different possibilities are also given for providing the low-wear sliding surface on the impeller. One of these consists of providing it through a wear-resistant coating of the corresponding regions of the impeller. Such a coating can be introduced, for example, by metal flame spraying. In addition, it is possible, in the region of the outer edge of the impeller on the back side, i.e., preferably on its corresponding axial end, to press a liner composed of a low-wear material onto its radial outer surface or onto a shoulder machined therein. Depending on the requirements and/or the costs to be borne for the respective application each time, such a liner may be composed, for example, of stainless steel, bronze, or another low-wear, i.e., particularly wear-resistant and corrosion-resistant material. Insofar as the pressure cap has a larger diameter than the impeller, it is also possible, however, to press a liner onto the back side of the impeller, a bearing race being connected to the liner and projecting radially from it, the bearing race being composed of a corresponding low-wear material. Of course, in the rotary pump according to the invention, without explaining it in more detail here, preferably the gap on the front side of the impeller, thus in the intake region of the pump is also completely sealed against a transport of material.

Examples of embodiment of the invention will be explained below based on the drawings. In the appended drawings are shown:

FIG. 1 a: A rotary pump having an arrangement for the gap sealing according to a first possible embodiment of the invention;

FIG. 1 b: The detail Z of FIG. 1 a;

FIG. 2 a: Another possible embodiment of the invention with gap sealing of a rotary pump in the back space of the impeller.

FIG. 2 b: The detail Z of FIG. 2 a;

FIG. 3 a: The sealing collar used in the embodiment according to FIG. 2 a or 2 b;

FIG. 3 b: The detail Z of FIG. 3 a.

FIG. 1 a shows a first possible embodiment of the invention with the seal according to the proposed solution formed in the gap region of the back space 6 of the impeller of a rotary pump for transporting liquids containing solids, the gap 3 in question being completely sealed against a transport of material due to this seal. The rotary pump is essentially composed of a pump housing 1, an impeller 2 taken up by the pump housing 1, the impeller being mounted on one side and driven in rotation by a shaft (not shown), and a pressure cap 12 sealing the pump housing 1 on the back side. The pump housing 1 encloses a flow space, through which flows the liquid containing solids that is to be transported or moved through the space by the rotating impeller 2 during operation of the pump. A media inlet opening 7 for the liquid to be transported opens up into an intake region 4 of this flow space, the liquid being discharged via a media outlet opening 8 in the pressure region 5 of the flow space, which radially surrounds the impeller. Further, the back space 6 of the impeller found on the side of the impeller 2 facing away from the intake region 4 is enclosed by the pump housing 1, which is closed here by the pressure cap 12. A sealing element 9 is fastened to the pressure cap 12. The sealing element 9 is composed of an elastomer, preferably polyurethane or rubber, which can be interlaced with fabric for stabilization. During operation of the pump, through the sealing element 9, whose elastic end 11 slides along on a low-wear sliding surface 10 of the impeller 2 formed in the region of the back side of the impeller, the gap 3 is completely sealed relative to the back space 6 of the impeller against a transport of material. Due to the type of design of the sealing element and its arrangement without labyrinths, secondary gaps or the like, as well as a depositing of solids or contaminants in the gap region are effectively prevented. Thus, it cannot lead to the buildup of such solids or contaminants on parts of the seal that are moved, and in this way, an undesired opening of the gap or in fact a braid formation does not occur, and thus lastly, there is no clogging of the pump with the consequence of damage to it.

In FIG. 1 b, which shows the detail Z of the embodiment shown in FIG. 1 a, it can be recognized that the sealing element 9 is designed here as an elastomeric sealing ring. This sealing ring tapers conically in an axial section 14. With its conically tapering section 14, the completely elastic sealing ring is pulled onto a section or shoulder of the pressure cap 12 projecting into the back space 6 of the impeller. With respect to the fact that the sealing ring forming the sealing element 9 contracts in its section 14 pulled onto the pressure cap 12, due to its elastic nature, the sealing element 9 is force-fitted onto the pressure cap 12 and thus may already be reliably fixed in place. Due to the fact that the axial section 14 of the sealing element 9, which is pulled onto the pressure cap 12, also tapers conically, however, in the example of embodiment shown, this force-fitting is additionally further supported by a form-fitting.

Further, it can be recognized in FIG. 1 b that a borehole 15 is formed, which extends in the radial direction r into the material of the pressure cap, behind the axial end of the sealing element 9 facing away from the impeller 2. This borehole 15 meets up with a second borehole 16 which extends in the axial direction a from the back space 6 of the impeller into the pressure cap 12. By means of such a running pair of boreholes 15, 16 and at least another second pair of boreholes 15′, 16′ disposed in the same way on another site in the periphery, channels are formed, which lead into the back space 6 of the impeller between impeller 2 and pressure cap 12. A pressure equilibration between the back space 6 of the impeller and the pressure region 5 of the flow space or an aerating and venting of the back space 6 of the impeller are provided via these channels, particularly with respect to a first filling of the rotary pump with the liquid to be transported. It is assured thereby that the sealing element 9 is not compressed in its shape and/or otherwise releases the gap 3 that has been sealed with its help in an undesired way either temporarily or permanently, due to possibly occurring pressure differences.

As can be recognized both from FIG. 1 a as well as from FIG. 1 b, in the embodiment example shown, the low-wear sliding surface 10 is formed in such a way that a liner 19*, which is joined with a bearing race 20* projecting in the radial direction, is pressed onto the impeller 2 in the region of the back side of the impeller. A difference that is present between the diameters of the impeller 2, on the one hand, and the pressure cap 12, on the other hand, is equilibrated by the bearing race 20. The outer periphery of the bearing race 20 composed of a low-wear material such as stainless steel or bronze, for example, forms the sliding surface 10 on which the corresponding elastic end 11 of the sealing element 9 slides along during the operation of the pump. These are not labeled in the figures.—Translator's note.

FIGS. 2 a and 2 b show another possible example of embodiment of the solution according to the invention having a somewhat differently configured sealing element 9 with respect to its shape. The sealing element 9 is formed here as an elastomeric collar gripping a shoulder of the pressure cap 12 from behind. In this example also, the diameter of the end of the pressure cap 12 projecting into the back space 6 of the impeller is larger than that of the impeller 2. The diameter difference given thereby, however, in this embodiment, is not equilibrated by a corresponding configuration of the elements serving for the formation of the sliding surface 10, but rather by a corresponding shaping of the sealing element 9, in the shape of an elastomeric sealing collar. The sealing collar has a section 21 extending in the radial direction r for this. The elastic end 11 of the sealing element 9, which is angled opposite to it and which slides along on the low-wear sliding surface 10, is connected to this section 21. The aerating and venting of the back space 6 of the impeller is provided presently in that on each of at least two positions relative to the periphery in the sealing collar, a passage 17, 17′, which projects through the radial section 21 of the sealing collar in the axial direction a, is provided. Simultaneously, the radially extending section 21 of the sealing collar is distanced slightly opposite the pressure cap 12 by at least two, preferably four supports 18, 18′ made of the material of the sealing collar, these supports being distributed on the periphery of this segment 21 and projecting in the axial direction a to the pressure cap 12. In this way, an aerating and venting of the back space 6 of the impeller is provided via the at least two passages 17, 17′ projecting through the radial section 21 of the sealing element 9 and a flat hollow space between the surface of the radial section 21 of the sealing collar facing the pressure cap 12 and the pressure cap 12. The sliding surface is presently formed in a circumferential channel of small depth machined in the impeller 2 on the back side of the impeller. In the region of this channel, the impeller 2 is either coated by a wear-resistant material or the sliding surface 10 is formed by pressing a wear-resistant ring into the channel.

Once more, the elastomeric sealing collar used in the embodiment according to FIGS. 2 a and 2 b is shown individually in FIGS. 3 a and 3 b, wherein FIG. 3 b relates to the detail Z of FIG. 3 a. Particularly well recognized in FIG. 3 a are the two passages 17, 17′ provided on opposite-lying peripheral positions in the sealing element 9 or in the sealing collar, and the supports 18, 18′ formed each time in the region of the passages and projecting in the axial direction. The corresponding formation is illustrated once more by the enlargement given in FIG. 3 b for the upper part of the sealing collar shown in FIG. 3 a.

LIST OF REFERENCE NUMBERS

1 Pump housing

2 Impeller

3 Gap

4 Intake region

5 Pressure region

6 Back space of the impeller

7 Media inlet opening

8 Media outlet opening

9 Sealing element

10 Sliding surface

11 Elastic end

12 Pressure cap

13 Axial section

14 Axial section

15, 15′ Borehole

16, 16′ Borehole

17, 17′ Passage

18, 18′ Support

19 Liner

20 Bearing race

21 Section 

1. A rotary pump for transporting liquids containing solids, with a pump housing having a media inlet opening and a media outlet opening for the liquid to be transported in each case, and an impeller disposed on a rotating driven shaft in the pump housing, wherein the pump housing encloses a flow space with an intake region on a front side of the impeller facing the media inlet opening and with a pressure region that surrounds the periphery of the impeller, as well as a back space of the impeller, which is formed on the side of the impeller facing away from the media inlet opening, is hereby characterized in that a structurally-imposed gap relative to the back space of the impeller is completely sealed opposite the flow space for the transported liquid with the solids contained therein by means of a sealing element that slides along by an elastic end on a low-wear sliding surface of the impeller, wherein, however, an aerating and venting of the back space of the impeller is given via a connection provided therefor to the pressure region of the flow space.
 2. The rotary pump according to claim 1, further characterized in that it involves a wastewater pump.
 3. An arrangement for gap sealing in a rotary pump for transporting liquids containing solids, having an impeller taken up by a pump housing, with an at least partially elastic sealing element and with a sliding surface, which is formed on the impeller and on which an elastic end of the sealing element slides along during the operation of the rotary pump, is hereby characterized in that the sealing element is fixed in place on a pressure cap closing the pump housing on the side facing away from an intake region of the rotary pump and the sliding surface is formed on the impeller in the region of a gap to a back space of the impeller on the side of the impeller facing away from the intake region and that the arrangement comprises means for aerating and venting the back space of the impeller.
 4. The arrangement according to claim 3, further characterized in that at least the end of the sealing element sliding along on the sliding surface of the impeller is composed of an elastomer.
 5. The arrangement according to claim 4, further characterized in that the regions of the sealing element composed of an elastomer are interlaced by a fabric, at least in sections.
 6. The arrangement according to claim 3, further characterized in that the sealing element is fixed in place on the pressure cap by means of an adhesive connection or by vulcanization.
 7. The arrangement according to claim 4, wherein the entire sealing element is composed of an elastomer, characterized in that the sealing element is fixed in place on the pressure cap in a force-fitting manner or in a force-fitting and form-fitting manner.
 8. The arrangement according to claim 7, further characterized in that the sealing element is formed as an elastomeric sealing ring, which slides along on the sliding surface of the impeller by a first axial segment forming the elastic end and is pulled onto a section or shoulder of the pressure cap projecting into the back space of the impeller by a second axial section.
 9. The arrangement according to claim 8, further characterized in that the axial section is conically tapered relative to its diameter.
 10. The arrangement according to claim 8, further characterized in that in the pressure cap relative to its periphery, there are formed on each of at least two positions a first borehole extending into the material of the pressure cap behind the axial section of the sealing element in the radial direction and a second borehole extending in the axial direction from the backspace of the impeller up to the first borehole, for the aerating and venting of the back space of the impeller.
 11. The arrangement according to claim 8, further characterized in that in the sealing element, which is formed as a sealing ring, relative to its periphery, there is formed on each of at least two positions a passage extending in the radial direction into the back space of the impeller, for the aerating and venting of the back space of the impeller.
 12. The arrangement according to claim 7, wherein an axial end of the pressure cap projecting into the back space of the impeller has a larger diameter than the impeller, further characterized in that the sealing element is formed as a sealing collar gripping a shoulder of the pressure cap from behind, this sealing collar having a section extending between pressure cap and impeller in the radial direction, for the equilibration of the different diameters.
 13. The arrangement according to claim 12, further characterized in that in the section of the sealing element formed as a sealing collar, extending in the radial direction relative to its periphery, there are formed on each of at least two positions a passage projecting through the section in question in the axial direction and a support composed of the material of the sealing collar and projecting in the axial direction onto the side facing the pressure cap, for the aerating and venting of the back space of the impeller.
 14. The arrangement according to claim 7, further characterized in that the sealing element for the additional fixation on the pressure cap is joined adhesively therewith via vulcanization.
 15. The arrangement according to claim 3, further characterized in that the low-wear sliding surface is provided by a wear-resistant coating of the impeller.
 16. The arrangement according to claim 3, further characterized in that for the formation of the sliding surface, a liner is pressed onto the periphery or onto a machined shoulder of the impeller on the side facing the back space of the impeller, the sliding surface being formed on the radial outer surface of the liner composed of a low-wear material.
 17. The arrangement according to claim 3, wherein an axial end of the pressure cap projecting into the back space of the impeller has a greater diameter than the impeller, characterized in that for the formation of the sliding surface, a liner is pressed onto the periphery or onto a machined shoulder of the impeller on the side facing the back space of the impeller, wherein the sliding surface on the radial outer surface of a bearing race connected to the liner, projecting opposite thereto in the radial direction is formed of a low-wear material. 